Synthetic and chemically defined media for cultivating microorganisms are well known. Conventional nutrient media for cultivating bacteria have been used to grow recombinant bacteria that are capable of producing heterologous polypeptides. Sources of amino acids such as yeast extract and casamino acids are usually included in high concentrations in the fermentation medium throughout the cultivation period. Such amino acids are expensive. Therefore it would be helpful to decrease the amount of supplemented amino acids in the fermentation medium while at the same time keeping expression of good quality desirable polypeptides at a high level.